Methods and apparatus for a variable-resolution screen

ABSTRACT

A variable-resolution screen apparatus and methodology for transforming an image from a microdisplay, display or projector into a variable-resolution image is described herein. The apparatus and methodology could take a high resolution part and a low resolution part, which could be created as a continuous stream of images that are masked to split into two, or as two interleaved images separated by time (or both). The two image streams are reassembled, the high resolution portion into the low resolution background, using various optical embodiments. The various embodiments use beam splitters, beam combiners, shutters, optical masks, lenses, mirrors, optical slabs, lens arrays and other optics in various combinations to create the variable-resolution image. The image from the microdisplay, display or projector is split (in some embodiments), transformed, and recombined to display on a screen or viewer&#39;s retina. This apparatus could be implemented in a virtual reality headset.

RELATED APPLICATIONS

None.

BACKGROUND Technical Field

The systems, apparatuses and methods described herein generally relateto video projection systems and, in particular, to video projectionsystems for near-eye displays, such as in virtual reality headsets.

Description of the Related Art

Since the early days of computing and television, display systems haverelied on displaying of visual information across a screen. Through theyears, processing power and miniaturization have allowed the screenresolution to increase dramatically, but the basic approach of uniformlydisplaying pixels across the screen has prevailed. However, thisapproach requires significant increases in communications andcomputational performance to deliver all of the pixels as the resolutionincreases. These problems have become particularly acute with the adventof virtual reality headsets, where the images, when viewed through, butnot limited to, an eyepiece or waveguide cover significant amount of theviewer's field of view compared to traditional displays and end uphaving some of their pixels usually or always in or near to the viewer'speripheral vision.

Traditional displays have pixels or scanlines with fixed sizes anddistances from each other in typically a regular grid or similaruniformly distributed pixel or scanline pattern on a flat or slightlycurved screen. See FIG. 1A which shows the single pixel 101 approach todisplay devices such as LCD (Liquid crystal display) or OLED (Organiclight-emitting diode) computer or television displays. FIG. 1B shows thescanline approach 102 used in other display devices such as CRT(Cathode-ray tube) computer or television displays and CRT or LBS (Laserbeam steering) video projectors. But the eye interprets the field ofvision 103 with high resolution at the center 104 and a decreased visionat the periphery 105, as seen in FIG. 1C.

Although human vision is quite different from the single pixel 101 orscanline 102 design with far more photoreceptor cells and visual acuityin the foveal vision 104, this kind of fixed and even distribution ofpixels or scanlines ensures a similar quality image when viewing everypart of a screen from many distances and angles.

Current examples where this uniform distribution of pixels or scanlinesdoes not apply is very limited and mostly unintentional, for example inthe projection mapping industry where often 3d surfaces are used as thescreens of video projectors.

Lately, a need for variable-resolution screens 103 has emerged becauseof increasing manufacturing costs of high resolution microdisplays,displays and projectors and much more demanding computational, bandwidthand storage requirements for display content created for traditionalscreens due to their increasing resolutions and fields of view,especially in virtual reality, augmented reality and mixed realityheadsets (from now on referred to as “XR headsets”).

Current XR headsets aim to provide a field of view close to the humanfield of view, which is on average 270 degrees horizontally by 135degrees vertically taking into account eye rotations and is usuallylower than that, for example 90 degrees horizontally by 100 degreesvertically for virtual reality headsets and lower than 50 degreeshorizontally by 50 degrees vertically for augmented reality headsetswhich is still higher than many screens at normal viewing distances suchas monitors, TVs and projection screens.

Other examples are video projectors that can be set up to project verywide and cover more of the viewer's field of view than with displaytechnologies such as CRT, LCD, OLED or microLED monitors and TVs andprojection screens at normal viewing distances.

A hybrid of the two is also a potential use case for this method anddisplay apparatus such as has been demonstrated by HMPDs (Head-MountedProjective Display) which are both a head-mounted device but projectonto a retroreflective projection screen like the ones used for videoprojectors rather than to a waveguide or projection screen viewed withan eyepiece lens or other optics similar to other XR headsets.

At such high fields of view, the same amount of pixels or scanlinesprovides less pixels or scanlines per degree of the field of view of theviewer and can suffer from noticeable lack of detail, pixelation andscreen-door effect or gap between scanlines.

Current methods of displaying less pixels in the periphery is done byhaving very high pixel density everywhere on the display and displayingless resolution on the pixels displayed near or in the viewer'speripheral vision rather than having less pixels or scanlines there tobegin with. This is a technique the Sony PlayStation VR and Oculus Gohead-mounted displays use (similar to 103).

This approach of increasing the pixel or scanline count on the displayuniformly poses both cost and computational challenges as way morepixels or scanlines are required to cover the high fields of view,especially for the average human field of view of 270 degreeshorizontally (195 degrees per eye) by 135 degrees vertically which for a60 pixels per degree resolution needed for a 20/20 vision would requireabout 11,700 pixels horizontally and 8100 pixels vertically per eye.

Manufacturing custom screens with more pixels where the viewer's fovealview can reach will be very expensive and require custom displaycontrollers.

Even if it were possible and economically feasible, the computationalpower required for creating real-time foveated content described abovefor such screens could be used for other tasks such as rendering anddisplaying more detailed virtual reality images in real-time.

So far methods have been proposed of optically combining two projectorsor displays to achieve variable-resolution screens such as with a beamsplitter. There are disadvantages to this approach such as higher cost,weight, size, requirement for color correction and synchronizationbetween different displays or projectors and only being able to have onehigh resolution part and one low resolution part on the image with twodisplays or projectors (see the teachings in the following patents:US20160240013A1, U.S. Pat. No. 9,711,072B1, U.S. Pat. No. 9,983,413B1,U.S. Pat. No. 9,989,774B1, U.S. Pat. No. 9,711,114B1, U.S. Pat. No.9,905,143B1).

Also, tilting beam splitters or steering an image with mirrors or prismsto reposition the high resolution area is challenging and results inperspective distortion and some optical aberrations which some of themethods described herein solve. Additionally, tilting or rotatingmechanical parts have disadvantages associated with mechanically movingparts which some of the methods described herein solve.

BRIEF SUMMARY OF THE INVENTION

An optical apparatus for creating a variable-resolution image stream ona screen is described herein that is made up of a projector connected toa video source, where the projector transmits a light image stream inthe form of a high resolution, small image component and a lowresolution, large image component. This light image stream is sent to animage steering element that directs the high resolution, small imagecomponent and the low resolution, large image component to a small imageoptical element and to a large image optical element. The opticalapparatus also includes an image separation element that separates thehigh resolution, small image component and the low resolution, largeimage component into a high resolution, small image stream and a lowresolution, large image stream, where the small image optical elementand the large image optical element focus the low resolution, largeimage stream and the high resolution, small image stream on the screensuch that the low resolution, large image stream and the highresolution, small image stream appear as the variable-resolution imagestream on the screen.

In some embodiments, the light image stream from the projector is timemultiplexed between the high resolution, small image component in afirst frame (frame n) and the low resolution, large image component in anext frame (frame n+1). The image separation element could be an opticalshutter to manage the time multiplexing. Alternately, the light imagestream from the projector could have the high resolution, small imagecomponent on one part of each image and a low resolution, large imagecomponent on another part of the image. The image separation elementcould be an optical mask (stencil) to support this embodiment.

In some embodiments, the screen is embedded in a virtual realityheadset. The small image optical element could include a lens array. Theimage steering element could be a rotating optical slab, mirrors, beamsplitter, wedge (Risley) prisms or optical masking elements. The largeimage optical element could be a lens or other optics that focuses thelow resolution, large image stream to an outer portion of the screen orviewer's field of view. The small image optical element could be a lensor other optics that focuses the high resolution, small image stream toa center portion of the screen or viewer's field of view.

An optical method creating a variable-resolution image stream on ascreen is described herein, where the method includes the steps ofcreating a light image stream in the form of a high resolution, smallimage component and a low resolution, large image component with aprojector connected to a video source; directing the high resolution,small image component and the low resolution, large image component,with an image or beam steering element, to a small image optical elementand to a large image optical element; separating the high resolution,small image component and the low resolution, large image component intoa high resolution, small image stream and a low resolution, large imagestream with an image separation element; and focusing, by the smallimage optical element and the large image optical element, the lowresolution, large image stream and the high resolution, small imagestream to form the variable-resolution image stream on the screen.

In some embodiments of the optical method, the light image stream fromthe projector is time multiplexed between the high resolution, smallimage component in a first frame (frame n) and the low resolution, largeimage component in a second frame (frame n+1). The separation of thesecomponents could be accomplished by using an optical shutter for theimage separation element. In another embodiment of the optical method,the light image stream from the projector could have the highresolution, small image component on one part of each image and a lowresolution, large image component on another part of the image, and theimage separation element could be an optical mask (stencil).

In some embodiments of the optical method, the screen is embedded in avirtual reality headset. The small image optical element could include alens array. The image steering element could be a rotating optical slab,mirrors, beam splitter, wedge (Risley) prisms or optical maskingelements. The large image optical element could be a lens or otheroptics that focuses the low resolution, large image stream to an outerportion of the screen or viewer's field of view. The small image opticalelement could be a lens or other optics that focuses the highresolution, small image stream to a center portion of the screen orviewer's field of view. The screen could be a diffuse projection screen,a retroreflective projection screen or a curved mirror or Fresnel mirrorwhich focuses a projection onto a viewer's retina (such as the ones usedin collimated display systems). The screen could also be a viewer'sretina. The projector could be a microdisplay or a display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the single pixel approach to display devices.

FIG. 1B shows the scanline approach to display devices.

FIG. 1C shows a muli-focus approach to a display.

FIG. 2 illustrates using persistence of vision to blend images from twoconsecutive frames into one final image.

FIG. 3 shows splitting an image of a microdisplay, display or projectorinto two parts that are combined.

FIG. 4A is a functional flow of the light through the optical functionsin the simplest embodiment.

FIG. 4B is a hardware flow of the light through the optical elements inthe simplest embodiment.

FIG. 5A is a functional flow of the light through the optical functionsin a slightly more complex embodiment.

FIG. 5B is a hardware flow of the light through the optical elements ina slightly more complex embodiment.

FIG. 5C is a hardware flow of the light through the optical elements asin the previous drawing with an optical mask (stencil).

FIG. 5D is a hardware flow of the light through the optical elements asin the FIG. 5B for each eye in a head-mounted display.

FIG. 5E illustrates an embodiment using optical slab elements.

FIG. 5F is a hardware flow of the light through the optical elements ina slightly more complex embodiment, using a screen.

FIG. 5G is a hardware flow of the light through the optical elements asin the previous drawing with an optical mask, using a screen.

FIG. 5H is a hardware flow of the light through the optical elements asin the FIG. 5F for each screen in a head-mounted display.

FIG. 6A shows an illustration with rectangles representing individualpixels.

FIG. 6B shows an illustration with individual pixels displaying anactual image.

FIG. 7A shows an original image.

FIG. 7B shows a perspective distorted image.

FIG. 8A shows the image with no distortion or distortion mismatchcorrected.

FIG. 8B shows the image with the distortion mismatch.

FIG. 9A shows light going through an optical slab.

FIG. 9B shows light going through an optical slab at an angle.

FIG. 9C shows light going through an optical slab at a different angle.

FIG. 9D shows a superimposition of light going through the same opticalslab at two opposite maximum angles.

FIG. 10A illustrates offsetting the image or beam with two mirrorstilted 45 degrees.

FIG. 10B illustrates offsetting the image or beam with two mirrorstilted 40 degrees.

FIG. 11 illustrates offsetting the image or beam with a set of fourmirrors.

FIG. 12 illustrates offsetting the image or beam with a set of Doveprism and four mirrors.

FIG. 13 shows a functional flow of light through the optical functionsin a lens array embodiment.

FIG. 14 shows a functional flow of light through the optical functionsin a second lens array embodiment.

FIG. 15 shows the light flow through the elements of one lens arrayembodiment.

FIGS. 16A and 16B illustrates an image (FIG. 16A) as it is seen on ascreen or viewer's retina (FIG. 16B) after using a lens array.

FIG. 17A shows an embodiment using a matched set of lens arrays and anoptical masking element.

FIG. 17B demonstrates reflective microdisplay used for the opticalmasking element.

FIG. 17C shows the use of a display, such as an LCD display with itsreflective and backlight layers removed as the optical masking element.

FIG. 17D illustrates the elements for generating an image with large andsmall parts that are already optically combined, with the ability tohide the duplicated images of the small part and show only one of them.

FIG. 17E shows the elements for generating an image with large and smallparts that are already optically combined, with the ability to hide theduplicated images of the small part and show only one of them.

FIG. 17F demonstrates the elements for another embodiments forgenerating an image with large and small parts that are alreadyoptically combined, with the ability to hide the duplicated images ofthe small part and show only one of them.

FIG. 17G presents another embodiments of the elements for generating animage with large and small parts that are already optically combined,with the ability to hide the duplicated images of the small part andshow only one of them.

FIG. 18 illustrates digitally and optically rearranging portions of animage.

FIG. 19 shows the portions of the images to be optically and digitallyrearranged do not have to be partitioned from the middle of the images.

FIG. 20 shows an embodiment of the mounting of the present inventions ina head-mounted display were the physical size is reduced.

FIG. 21 shows an embodiment of the mounting of the present inventions ina head-mounted display using a mirror to reduce the physical size of theunit.

FIG. 22 shows an embodiment of the mounting of the present inventions ina head-mounted display using a mirror and a beam splitter to reduce thephysical size of the unit.

DETAILED DESCRIPTION

The present inventions describe a system and method for implementing avariable-resolution screen, where the area in front of the viewer'sfield of view, where the foveal vision expects the greatest resolution,are in a higher resolution than the areas of the screen on theperiphery, where the peripheral vision expects less resolution andclarity. In this application four major (and many minor) embodiments aredescribed.

The following inventions describe a method and display apparatus forachieving a variable-resolution screen, which can be defined as a screenwhich allows the image, when viewed directly or by, but not limited to,an eyepiece (the lens closest to the viewer's eye) or waveguide, providea resolution which is not uniform across the image but rather morepixels or scanlines are visible to the viewer where needed on the image,such as the center of the viewer's field of view and less in other partor parts of the image.

Such a screen is different from existing screens displaying pre-renderedor real time-rendered foveated content as such methods ofvariable-resolution content display limit the high resolution part ofthe content to the native resolution possible with that part of thescreen. The term “screen” can also be used to describe the viewer'sretina.

Foveated content is an image, video or real time-generated images whereon each image the resolution varies across the image, for example toshow more resolution only where the viewer is looking, is able to lookat or is meant to look at.

The variable-resolution screen methods and apparatus described hereallow to achieve more resolution visible in one or more parts of theimage than is possible with the microdisplay, display or projector whenused without the methods described here.

The methods described need only existing computing hardware such as aPC, mobile phone or tablet to provide the pre-rendered or realtime-rendered content for it.

The methods require as little as only a single DLP (Digital lightprocessing), LCoS (Liquid crystal on silicon), LCD (Liquid crystaldisplay), OLED (Organic light-emitting diode), MicroLED or similarmicrodisplay, display or projector or LBS (Laser beam steering) orsimilar projector 401, 411, 501, 511, 521, 551, 2301, 5111, 5121, 5151,1401 for one variable-resolution screen or one of the above for onevariable-resolution screen per eye, for example for head-mounteddisplays. Using as little as only a single microdisplay, display orprojector or only one per eye allows to minimize the cost of producingsuch a variable-resolution screen apparatus, reduce weight and size ofthe apparatus. A single microdisplay, display or projector can alsorefer to microdisplays, displays or projectors where a separate displayor microdisplay panel is used for each color channel and they areoptically combined such as with a trichroic prism, X-cube prism ordichroic filters. This can be useful for various reasons such aseliminating color separation (also known as “rainbow artifact”) andincreasing the refresh rate.

The usage of such variable-resolution screens are, but not limited to,virtual reality, augmented reality and mixed reality headsets (“XRheadsets”) and video projectors.

Positioning with Mirrors or Wedge Prisms of a High Resolution SmallImage Over a Low Resolution Large Image

In one embodiment, a variable-resolution screen can be achieved bypositioning a high resolution small image over a low resolution largeimage with mirrors or wedge (Risley) prisms.

To achieve a variable-resolution screen a single display technology suchas a microdisplay or display 401, 411, 501, 511, 521, 551 is operated atfast refresh rates. Each consecutive frame (frame n+1) the microdisplayor display is used to either display a small high resolution part 204 orparts of the final image 205 or a large low resolution part 203 or partsof the final image 205 by sharing the refresh rate of the frames 201,202 and final image 205 between the latter's two or more parts 203, 204.Persistence of vision blends the two parts 203, 204 into one final image205. See FIG. 2.

In FIG. 2, the frames alternate with the low resolution frame n 201displayed followed by high resolution frame n+1 202. With a sufficientrefresh rate, the eye interprets the two as a single image 205. The lowresolution portion of the combined screen 203 could have a neutral color(black) in the high resolution area 204. And the high resolution portionof the combined screen 204 could have a neutral color (black) in the lowresolution area 203. A slight overlap between the two regions 203, 204will prevent a noticeable seam or gaps by having a blend region whereregions 203, 204 overlap. In another embodiment, the low resolutionsection 203 is not masked and blends with the high resolution portion204 in the area where the high resolution resides.

Alternatively, to achieve a variable-resolution screen a single displaytechnology such as a microdisplay or display is optically split into twoor more parts 301, 302. This method allows one part 301 or parts to usemore pixels on the final image by sacrificing the resolution of anotherpart 302 or parts on the final image. See FIG. 3.

The two methods can also be combined to allow to create more parts onthe final image or to allow to create two or more final images bysharing both the resolution and refresh rate of the microdisplay ordisplay between the parts, such as for using a single microdisplay ordisplay to create final images for both eyes in a head-mounted display.

In FIG. 3, a 16:9 aspect ratio microdisplay or display split into twoparts 301, 302 is shown, for example 1920×1080 pixel microdisplay ordisplay split into a small 1080×1080 pixel high resolution part 301 anda large 840×1080 pixel low resolution part 302 (the latter may then beoptically flipped 90 degrees for a better aspect ratio).

Using optical or optical and mechanical and also optionally digitalmethods, the parts 301 and 302 can be resized and superimposed on eachother 305. The large low resolution part 303 can be masked where thesmall high resolution part is 304 and where they overlap.

The masking can further be made more seamless by blending the edgesoptically or digitally by making the transition less abrupt with adigital resolution falloff in the high resolution small image or dimmingthe pixels with a falloff on both images.

The brightness levels between the two parts may be balanced opticallysuch as with neutral density filters or digitally.

Look to FIGS. 4A and 4B. To be able to use the same microdisplay ordisplay 401, 411 for each part which have a different size and positionon the final image 405, with the first method from FIG. 2, the image ofthe microdisplay or display is steered with a steering elementoptomechanically or optically, such as, but not limited to, a rotatingmirror or beam splitter 402, 412 and an optional mirror 413, only to oneof two optical elements 403, 404, 414, 415 for each frame. In case ofusing a beam splitter instead of a rotating mirror as the steeringelement, each image each frame must be blocked or let to passaccordingly before, inside or after the optical element 403, 404, 414,415 with an optical or mechanical shutter such as an LCD shutter inorder to prevent 403, 414 and 404, 415 from receiving the same image ofevery frame instead of the different images of different consecutiveframes. This is of course not needed if a polarizer beam splitter isused and the polarization of the image can be controlled each framebefore it reaches the beam splitter, such as with a switchable liquidcrystal polarization rotator.

To be able to use the same microdisplay or display 401, 411 for eachpart which have a different size and position on the final image 405,with the second method from FIG. 3, the image of the microdisplay ordisplay 401, 411 is steered with a steering element such as, but notlimited to, a beam splitter or a mirror on an image plane 402, 412 andan optional mirror 413, to two optical elements 403, 404, 414, 415. Incase of using a beam splitter and not a mirror on an image plane, eachimage is then masked accordingly before, inside or after the opticalelement 403, 404, 414, 415 with an optical masking element such as astencil. The mirror or stencil must be on an image plane to create asharp cut.

Steering element 402, 412 may be, but is not limited to, a mirror,mirrors, beam splitter and optical or mechanical shutter or shutterscombined with one of the above.

The optical element 403, 404, 414, 415 may be, but is not limited to,one of the following, or a combination of: lenses, mirrors, prisms,free-form mirrors.

One of the optical elements 404, 415 may create a small image 417 andthe other optical element 403, 414 a comparably large image 416.

In FIG. 4A, the microdisplay or display 401 creates the image andoptically sends it to the image or beam steering element 402. The imagesteering element 402 splits the image into two (or more) images, sendingthe images to optics creating the low resolution, large image 403 and ahigh resolution, small image 404. The optical output of the optics 403,404 are sent to a screen 418 or onto the viewer's retina where the finalimage is created 405.

Looking to FIG. 4B, the microdisplay or display 411 creates an imagethat is split with a beam splitter (such as half silvered mirror orpolarizer beam splitter) 412 into two identical images going indifferent directions. One is directed to optics which create a largeimage 414, while the other goes through a mirror 413 to another opticswhich creates a small image 415. The large image optics 414 create thelower resolution image 416. The small image optics 415 creates thehigher resolution image 417. Both the lower 416 and higher 417resolution images are projected on the screen 418 or on the viewer'sretina as seen in FIG. 5B.

Masking of the area of the large image 416 where the small image 417 iscan be achieved, again, digitally, by having black pixels displayedthere, or optically, for example by having a stencil on an image planesomewhere inside, before or after the optics to physically (optically)mask off that part of the image.

Then, optionally, the positioning of the small image can be achievedwith, but not limited to one or more of the following: actuators withmirrors, galvanometer scanners, actuators with wedge (Risley) prisms,actuators with tilting or shifting lenses, as seen in FIG. 5A.

FIG. 5A shows a microdisplay or display 501 creating an image that issent to an image or beam steering element 502 (could be a beamsplitter). One of the two identical images is sent to the large imageoptical element 503 and the other image is sent to the small imageoptical element 504. The small image optical element 504 sends the imageto an image or beam steering element 506 (could be a mirror). The imagesare then combined into a final image 505.

The two images are optically combined, such as with a beam splitter andviewed directly, or through, but not limited to, an eyepiece orwaveguide.

Looking to FIG. 5B, the optical elements are shown. The microdisplay ordisplay 511 sends the image to a beam splitter or a rotating mirror 512,that sends images to the large image optics 514 and to a mirror 513 thatredirects the image to the small image optics 515. From the small imageoptics 515, the image is sent to a mirror 519 and then to a beamcombiner 518 (beam splitter) to combine with the output of the largeimage optics 514. From the beam combiner 518, the large image 516 andthe small image 517, are sent as a combined image to the viewer's retina510. In case of using a beam splitter instead of a rotating mirror asthe steering element, each image each frame must be blocked or let topass accordingly before, inside or after the optical element 514, 515with an optical or mechanical shutter such as an LCD shutter in order toprevent 514 and 515 from receiving the same image of every frame insteadof the different images of different consecutive frames. This is ofcourse not needed if a polarizer beam splitter is used and thepolarization of the image can be controlled each frame before it reachesthe beam splitter, such as with a switchable liquid crystal polarizationrotator.

One difference between FIGS. 5B and 5C is that images are illustrated astwo lines rather than one before reaching the optical masking elements.This is done to illustrate how the image is masked/cropped by theoptical masking elements 530, 531.

Looking to FIG. 5C, the optical elements are shown, for processing theimage structure in FIG. 3. The microdisplay or display 521 sends theimages to a beam splitter 522, that sends two identical images, one to amirror 523 first, to optical masking elements (stencils, physicalbarriers to hide part of the image) 530, 531. The stencil must be on animage plane to create a sharp cut, so can also be inside the optics (524and 525), or after the optics.

The images leave from the stencils 530, 531 to the large image optics524 and to the small image optics 525. From the small image optics 525,the image is sent to a mirror 529 and then to a beam combiner 528 (beamsplitter) to combine with the output of the large image optics 524. Fromthe beam combiner 528, the large image 526 and the small image 527, aresent as a combined image to the viewer's retina 520.

Looking to FIG. 5D we see a head-mounted display embodiment which uses asingle microdisplay or display 551 for both eyes. First the resolutionof the microdisplay or display is split between eyes, then each frame isused only for one projection (large or small image). For example with a240 Hz DLP microdisplay this provides 120 Hz refresh rate per image pereye.

The microdisplay or display 551 sends the image to a beam splitter 560that sends two identical images, one to a mirror 580 first, to thestencils 561, 571 that mask off the portion of the image not destinedfor the specific eye. In one embodiment, the stencils 561, 571 could beshutters such as an LCD shutter or LCD pi-cell so each frame will besent only to one optics and blocked for the rest of the optics 554, 555,574, 575, such as in the instance seen in FIG. 2. In another embodiment,the stencils 561, 571 could be removed so each frame the whole imagewill be sent only to one optics and blocked for the rest of the optics554, 555, 574, 575, such as in the instance seen in FIG. 2. For examplewith a 240 Hz DLP microdisplay this provides 60 Hz refresh rate perimage per eye.

The left stencil (top in the diagram) 561 sends the image to a secondbeam splitter 552 which send two identical images, one to a mirror 553first, to the two LCD shutters 562, 563 for the FIG. 2 embodiment. Theshutters 562, 563 could be replaced with stencils (a physical barrier tohide part of the image) for the FIG. 3 embodiment. The stencils have tobe on an image plane to create a sharp cut, so can also be inside theoptics (554 and 555), or after the optics.

The images leave from the shutters (or stencils) 562, 563 to the largeimage optics 554 and to the small image optics 555. From the small imageoptics 555, the image is sent to a mirror 559 and then to a beamcombiner 558 (beam splitter) to combine with the output of the largeimage optics 554. From the beam combiner 558, the large image 556 andthe small image 557, are sent as a combined image to the viewer's retina550.

The right stencil (bottom in the diagram) 571 sends the image to asecond beam splitter 572 which sends two identical images, one to amirror 573 first, to the two LCD shutters 580, 581 for the FIG. 2embodiment. The shutters 580, 581 could be replaced with stencils forthe FIG. 3 embodiment. The stencils must be on an image plane to createa sharp cut, so can also be inside the optics (574 and 575), or afterthe optics.

The images leave from the shutters (or stencils) 580, 581 to the largeimage optics 574 and to the small image optics 575. From the small imageoptics 575, the image is sent to a mirror 579 and then to a beamcombiner 578 (beam splitter) to combine with the output of the largeimage optics 574. From the beam combiner 578, the large image 576 andthe small image 577, are sent as a combined image to the viewer's retina570.

Due to persistence of vision with the method in FIG. 2 and masking withthe method in FIG. 3 the two parts appear as one uniform image 604 inFIG. 6B.

In FIG. 6A, the illustration shows rectangles representing individualpixels 601. FIG. 6B shows an illustration with individual pixelsdisplaying an actual image 604.

Since the small high resolution part 603, 606 in the final image 601,604 can be smaller than it could be without the use of these methods,the variable-resolution screen method and apparatus described hereallows to achieve more resolution visible in one or more parts of theimage than is possible with the display technology when used without themethods described here.

This allows to achieve a variable-resolution screen, such as ahead-mounted display screen which uses only one microdisplay or displayor one per eye with a high pixel or scanline density in the center ofthe field of view of the viewer and less in the periphery.

Optionally, by adding eye tracking via, but not limited to, gazetracking cameras or electrodes, the small high resolution part 603, 606can be positioned on the final image 601, 604 on the large lowresolution part 602, 605 where the viewer's foveal view is at any givenpoint in time. This allows to always have more pixels or scanlinesconcentrated in the foveal and optionally also in the near peripheralview of the viewer at any given point in time.

Optionally the positioning of the large low resolution part 602, 605 canbe achieved the same way the positioning of the small high resolutionpart 603, 606, for example to have pixels only in the field of view ofthe viewer's eye and not the total field of view of the viewer whichtakes into account eye rotations.

There can also be more than two parts, such as three, one for the fovealview, one for near peripheral and one for far peripheral and they can becombined and optionally positioned the same way as mentioned above.

Those skilled in the art will understand that the order of some elementscan be changed and more can be added, such as steering both large andsmall images together after they are optically combined, or adding moreelements for creating more small or large parts on the final image.

Positioning with Mirrors or Wedge Prisms of a High Resolution NarrowProjection Beam Over a Low Resolution Wide Projection Beam

In another embodiment, a variable-resolution screen is achieved bypositioning a high resolution narrow video projection over a lowresolution wide video projection with mirrors or wedge (Risley) prisms.

To achieve a variable-resolution screen a single video projector such asa single illuminated microdisplay, display, LBS (Laser beam steering)projector or other type of video projector (from now on referred to as“projector”) 401, 411, 501, 511, 521, 551, 5111, 5121, 5151 is operatedat fast refresh rates. Each consecutive frame (frame n+1) the projectoris used to either display a small high resolution part 204 or parts ofthe final image 205 or a large low resolution part 203 or parts of thefinal image 205 by sharing the refresh rate of the frames 201, 202 andfinal image 205 between the latter's two or more parts 203, 204.Persistence of vision blends the two parts 203, 204 into one finalprojected image 205.

Alternatively, in FIG. 3, to achieve a variable-resolution screen 305 asingle video projector such as a single illuminated microdisplay,display, LBS (laser beam steering) projector or other type of videoprojector (from now on referred to as “projector”) is optically splitinto two or more parts 301, 302. This method allows one part 301, 304 orparts to use more pixels on the final projected image 305 by sacrificingthe resolution of another part 302, 303 or parts.

The two methods can also be combined to allow to create more parts onthe final projected image or to allow to create two or more finalprojected images by sharing both the resolution and refresh rate of theprojector between the parts, such as for using a single projector tocreate final projected images for both eyes in a head-mounted display.

There are several advantages to using projection beams rather thanmicrodisplays and displays when viewed directly or through lens or otheroptics:

First of all, it is very challenging to design a wide field of viewhead-mounted display when using microdisplays while trying to keep themagnification lenses or other optics small and lightweight versus usingmuch smaller projection lenses to project onto a screen larger than themicrodisplay and viewing that screen through lenses or other opticsinstead.

Second, using video projections has the advantage of allowing to haveall of the optical elements including steering elements be much smalleras they can be positioned in the optical design before, or somewhere inbetween the projection optics which create the large final image on aprojection screen.

Third, due to the external illumination nature of reflectivemicrodisplays such as LCoS, DLP and transmissive microdisplays such asLCD, the beam angle for each pixel can be narrower than with emissivemicrodisplays such as OLED or microLED which can allow to provide anoptical system with less stray light and be more efficient whileproviding the same or higher brightness to the viewer.

Fourth, due to the external illumination nature of reflective andtransmissive microdisplays much higher brightness is achievable thanwith emissive microdisplays which have the physical pixels emit thelight themselves like OLEDs and microLEDs or with LCD displays whichmakes it challenging to have them provide enough brightness, especiallyas the field of view and magnification of the display increases, or foraugmented reality head-mounted displays where there can be a lot oflight loss in the optical system.

In FIG. 3, a single 16:9 aspect ratio microdisplay or display is splitinto two parts, for example 1920×1080 pixel microdisplay or displaysplit into a small 1080×1080 pixel high resolution part 301 and a large840×1080 pixel low resolution part 302 (the latter may then be opticallyflipped 90 degrees for a better aspect ratio).

Using optical or optical and mechanical and also optionally digitalmethods, the parts 301 and 302 can be resized and superimposed on eachother 305 and the large low resolution part 303 can be masked where thesmall high resolution part 304 is and where they overlap.

The masking can further be made more seamless by blending the edgesoptically or digitally by making the transition less abrupt with adigital resolution falloff in the high resolution small image or dimmingthe pixels with a falloff on both images.

The brightness levels between the two parts may be balanced opticallysuch as with neutral density filters or digitally.

Look to FIGS. 4A and 4B. To be able to use the same projector 401, 411for each part which have a different size and position on the finalprojected image 405, with the first method from FIG. 2, the beam of theprojector is steered with a steering element optomechanically oroptically, such as, but not limited to, a rotating mirror or beamsplitter 402, 412 and an optional mirror 413, only to one of two opticalelements 403, 404, 414, 415 for each frame. In case of using a beamsplitter instead of a rotating mirror as the steering element, each beameach frame must be blocked or let to pass accordingly before, inside orafter the optical element 403, 404, 414, 415 with an optical ormechanical shutter such as an LCD shutter in order to prevent 403, 414and 404, 415 from receiving the same beam of every frame instead of thedifferent beams of different consecutive frames. This is of course notneeded if a polarizer beam splitter is used and the polarization of thebeam can be controlled each frame before it reaches the beam splitter,such as with a switchable liquid crystal polarization rotator.

To be able to use the same projector 401, 411 for each part which have adifferent size and position on the final image 405 on the screen 418,with the second method from FIG. 3, the beam of the projector 401, 411is steered with a steering element such as, but not limited to, a beamsplitter or a mirror on an image plane 402, 412 and an optional mirror413, to two optical elements 403, 404, 414, 415. In case of using a beamsplitter and not a mirror on an image plane, each beam is then maskedaccordingly before, inside or after the optical element 403, 404, 414,415 with an optical masking element such as a stencil. The mirror orstencil must be on an image plane to create a sharp cut.

Steering element 402, 412 may be, but is not limited to, a mirror,mirrors, beam splitter and optical or mechanical shutter or shutterscombined with one of the above.

The optical element 403, 404, 414, 415 may be, but is not limited to,one of the following, or a combination of: lenses, mirrors, prisms,free-form mirrors.

One of the optical elements 404, 415 may create a narrow beam 417 andthe other optical element 403, 414 a comparably wide beam 416.

Looking to FIG. 4B, the projector 411 creates a projection beam that issplit with a beam splitter (such as half silvered mirror or polarizerbeam splitter) 412 into two identical projection beams going indifferent directions. One is directed to optics 414 which create a widebeam, while the other goes through a mirror 413 to another optics 415which creates a narrow beam. The wide beam optics 414 create the lowerresolution image beam 416. The narrow beam optics 415 creates the higherresolution image beam 417. Both the lower 416 and higher 417 resolutionbeams are projected onto the viewer's retina or screen 418.

Masking of the area of the wide beam 416 where the narrow beam 417 iscan be achieved, again, digitally by having black pixels displayedthere, or optically, for example by having a stencil on an image planesomewhere inside, before or after the optics to physically (optically)mask off that part of the projection beam.

Then, optionally, the positioning of the small image of the narrow beamcan be achieved with, but not limited to one or more of the following:actuators with mirrors, galvanometer scanners, actuators with wedge(Risley) prisms, actuators with tilting or shifting lenses, as seen inFIG. 5A.

The two beams are projected onto the same screen as seen in FIG. 4B orfirst optically combined, such as with a beam splitter, projected onto ascreen and viewed directly, or through, but not limited to, an eyepieceor waveguide. This is seen in the beam steering elements 519 and 518 ofFIG. 5B.

Looking to FIG. 5F, the optical elements are shown. The projector 5111sends the projection beam to a beam splitter or a rotating mirror 5112,that sends projection beams to the wide beam optics 5114 and to a mirror5113 that redirects the projection beam to the narrow beam optics 5115.From the narrow beam optics 5115, the beam is sent to a mirror 5119 andthen to a beam combiner 5118 (beam splitter) to combine with the outputof the wide beam optics 5114. From the beam combiner 5118, the wide beam5116 and the narrow beam 5117, are sent as a combined projection beam tothe viewer's retina or the screen 5110. In case of using a beam splitterinstead of a rotating mirror as the steering element, each beam eachframe must be blocked or let to pass accordingly before, inside or afterthe optical element 5114, 5115 with an optical or mechanical shuttersuch as an LCD shutter in order to prevent 5114 and 5115 from receivingthe same beam of every frame instead of the different beams of differentconsecutive frames. This is of course not needed if a polarizer beamsplitter is used and the polarization of the image can be controlledeach frame before it reaches the beam splitter, such as with aswitchable liquid crystal polarization rotator.

One difference between FIGS. 5F and 5G is that projection beams areillustrated as two lines rather than one before reaching the opticalmasking elements. This is done to illustrate how the projection beam ismasked/cropped by the optical masking elements 5130, 5131.

Looking to FIG. 5G, the optical elements are shown, for processing theimage structure in FIG. 3. The projector 5121 sends the projection beamto a beam splitter 5122, that sends two identical projection beams, oneto a mirror 5123 first, to a stencil (a physical barrier to hide part ofthe image) 5130, 5131. The stencils must be on an image plane to createa sharp cut, so can also be inside the optics (5124 and 5125), or afterthe optics.

The beams leave from the stencils 5130, 5131 to the wide beam optics5124 and to the narrow beam optics 5125. From the narrow beam optics5125, the beam is sent to a mirror 5129 and then to a beam combiner 5128(beam splitter) to combine with the output of the wide beam optics 5124.From the beam combiner 5128, the wide beam 5126 and the narrow beam5127, are sent as a combined projection beam to the viewer's retina orscreen 5120.

Looking to FIG. 5H we see a head-mounted display embodiment which uses asingle projector 5151 for both screens (for both eyes). First theresolution of the microdisplay or display is split between eyes, theneach frame is used only for one projection (large or small image). Forexample with a 240 Hz DLP projector this provides 120 Hz refresh rateper image per screen.

The projector 5151 sends the beam to a beam splitter 5160 that sends twoidentical beams, one reflected from a mirror 5182 first, to the stencils5161, 5171 that mask off the portion of the image not destined for thespecific eye. In one embodiment, the stencils 5161, 5171 could beshutters such as an LCD shutter or LCD pi-cell, so each frame will besent only to one optics and blocked for the rest of the optics 5154,5155, 5174, 5175, such as in the instance seen in FIG. 2. In anotherembodiment, the stencils 5161, 5171 could be removed so each frame thewhole image will be sent only to one optics and blocked for the rest ofthe optics 5154, 5155, 5174, 5175, such as in the instance seen in FIG.2. For example with a 240 Hz DLP projector this provides 60 Hz refreshrate per image per eye.

The left stencil (top in the diagram) 5161 sends the beam to a secondbeam splitter 5152 which send two identical beams, one to a mirror 5153first, to the two LCD shutters 5162, 5163 for the FIG. 2 embodiment. TheLCD shutters 5162, 5163 could be replaced with stencils (a physicalbarrier to hide part of the projection beam) for the FIG. 3 embodiment.The stencils must be on an image plane to create a sharp cut, so canalso be inside the optics (5154 and 5155), or after the optics.

The beams leave from the shutters (or stencils) 5162, 5163 to the widebeam optics 5154 and narrow beam optics 5155. From the narrow beamoptics 5155, the beam is sent to a mirror 5159 and then to a beamcombiner 5158 (beam splitter) to combine with the output of the widebeam optics 5154. From the beam combiner 5158, the wide beam 5156 andthe narrow beam 5157, are sent as a combined beam to the screen 5150 orviewer's retina.

The right stencil (bottom in the diagram) 5171 sends the beam to asecond beam splitter 5172 which sends two identical beams, one to amirror 5173 first, to the two LCD shutters 5180, 5181 for the FIG. 2embodiment. The LCD shutters 5180, 5181 could be replaced with stencils(a physical barrier to hide part of the projection beam) for the FIG. 3embodiment. This has to be in an image plane to create a sharp cut, socan also be inside the optics (5174 and 5175), or after the optics.

The beams leave from the LCD shutters (or stencils) 5180, 5181 to thewide beam optics 5174 and narrow beam optics 5175. From the narrow beamoptics 5175, the beam is sent to a mirror 5179 and then to a beamcombiner 5178 (beam splitter) to combine with the output of the widebeam optics 5174. From the beam combiner 5178, the wide beam 5176 andthe narrow beam 5177, are sent as a combined beam to the screen 5170 orviewer's retina.

Due to persistence of vision with the method in FIG. 2 and masking withthe method in FIG. 3 the two parts appear as one uniform projected image604 in FIG. 6B.

In FIG. 6A, the illustration shows rectangles representing individualpixels 601. FIG. 6B shows an illustration with individual pixelsdisplaying an actual image 604.

Since the small high resolution part 603, 606 in the final projectedimage 601, 604 can be smaller than it could be without the use of thesemethods, the variable-resolution screen method and apparatus describedhere allows to achieve more resolution visible in one or more parts ofthe projected image than is possible with the projector when usedwithout the methods described here.

This allows to achieve a variable-resolution screen, such as ahead-mounted display screen which uses only one projector or one per eyewith a high pixel or scanline density in the center of the field of viewof the viewer and less in the periphery.

Optionally, by adding eye tracking via, but not limited to, gazetracking cameras or electrodes, the small high resolution part 603, 606can be positioned on the final projected image 601, 604 on the large lowresolution part 602, 605 where the viewer's foveal view is at any givenpoint in time. This allows to always have more pixels or scanlinesconcentrated in the foveal and optionally also in the near peripheralview of the viewer at any given point in time.

Optionally the positioning of the large low resolution part 602, 605 canbe achieved the same way the positioning of the small high resolutionpart 603, 606, for example to have pixels only in the field of view ofthe viewer's eye and not the total field of view of the viewer whichtakes into account eye rotations.

There can also be more than two parts, such as three, one for the fovealview, one for near peripheral and one for far peripheral and they can becombined and optionally positioned the same way as mentioned above.

Those skilled in the art will understand that the order of some elementscan be changed and more can be added, such as steering both large andsmall images together after they are optically combined, or adding moreelements for creating more small or large parts on the final projectedimage.

Shifting with Optical Slabs or Mirrors a High Resolution Small Image orNarrow Projection Beam Over a Low Resolution Large Image or WideProjection Beam

In another embodiment, a variable-resolution screen is achieved byshifting/offsetting a small and high resolution image or projection beamover a large and low resolution image or projection beam with opticalslabs or mirrors.

To achieve a variable-resolution screen a single display technology suchas a microdisplay or display or a single video projector such as asingle illuminated microdisplay, display, LBS (laser beam steering)projector or other type of video projector (from now on referred to as“projector”) 401, 411, 501, 511, 521, 551, 2301, 5111, 5121, 5151 isoperated at fast refresh rates. In FIG. 2, each consecutive frame (framen+1) the microdisplay, display or projector is used to either display orproject a small high resolution part 204 or parts of the final image 205or a large low resolution part 203 or parts of the final image 205 bysharing the refresh rate of the frames 201, 202 and final image 205between the latter's two or more parts 203, 204. Persistence of visionblends the two parts 203, 204 into one final image 205.

FIG. 3 shows an alternative embodiment, to achieve a variable-resolutionscreen a single display technology such as a microdisplay, display or asingle video projector such as a single illuminated microdisplay,display, LBS (Laser beam steering) projector or other type of videoprojector (from now on referred to as “projector”) is optically splitinto two or more parts 301, 302. This method allows a small highresolution part or parts 304 to use more pixels on the final image 305by sacrificing the resolution of a large low resolution part 303 orparts.

The two methods can also be combined to allow to create more parts onthe final image or to allow to create two or more final images bysharing both the resolution and refresh rate of the microdisplay,display or projector between the parts, such as for using a singlemicrodisplay, display or projector to create final images for both eyesin a head-mounted display.

In FIG. 3, a single 16:9 aspect ratio microdisplay or display is splitinto two parts, for example 1920×1080 pixel microdisplay or displaysplit into a small 1080×1080 pixel high resolution part 301 and a large840×1080 pixel low resolution part 302 (the latter may then be opticallyflipped 90 degrees for a better aspect ratio).

Using optical or optical and mechanical and also optionally digitalmethods, the parts 301 and 302 can be resized and superimposed on eachother and the large low resolution part 303 can be masked where thesmall high resolution part 304 is and where they overlap.

The masking can further be made more seamless by blending the edgesoptically or digitally by making the transition less abrupt with adigital resolution falloff in the high resolution small image 304 ornarrow beam or dimming the pixels with a falloff on both images orbeams.

The brightness levels between the two parts may be balanced opticallysuch as with neutral density filters or digitally.

Look to FIGS. 4A and 4B. To be able to use the same microdisplay,display or projector 401, 411 for each part which have a different sizeand position on the final image 405, with the first method from FIG. 2,the image of the microdisplay or display or the beam of the projector issteered with a steering element optomechanically or optically, such as,but not limited to, a rotating mirror or beam splitter 402, 412 and anoptional mirror 413, only to one of two optical elements 403, 404, 414,415 for each frame. In case of using a beam splitter instead of arotating mirror as the steering element, each image or beam each framemust be blocked or let to pass accordingly before, inside or after theoptical element 403, 404, 414, 415 with an optical or mechanical shuttersuch as an LCD shutter in order to prevent 403, 414 and 404, 415 fromreceiving the same image or beam of every frame instead of the differentimages or beams of different consecutive frames. This is of course notneeded if a polarizer beam splitter is used and the polarization of thebeam can be controlled each frame before it reaches the beam splitter,such as with a switchable liquid crystal polarization rotator.

To be able to use the same microdisplay, display or projector 401, 411for each part which have a different size and position on the finalimage 405 with the second method from FIG. 3, the image of themicrodisplay or display or the beam of the projector 401, 411 is steeredwith a steering element such as, but not limited to, a beam splitter ora mirror on an image plane 402, 412 and an optional mirror 413, to twooptical elements 403, 404, 414, 415. In case of using a beam splitterand not a mirror on an image plane, each image or beam is then maskedaccordingly before, inside or after the optical element 403, 404, 414,415 with an optical masking element such as a stencil. The mirror orstencil must be on an image plane to create a sharp cut.

Steering element 402, 412 may be, but is not limited to, a mirror,mirrors, beam splitter and optical or mechanical shutter or shutterscombined with one of the above.

The optical element 403, 404, 414, 415 may be, but is not limited to,one of the following, or a combination of: lenses, mirrors, prisms,free-form mirrors.

One of the optical elements 404, 415 may create a small image or narrowbeam 417 and the other optical element 403, 414 a comparably large imageor wide beam 416.

In the embodiment in FIGS. 5A and 5B, the positioning of the small imageor narrow beam can be achieved with, but not limited to one or more ofthe following: optical slabs or mirrors 506, 519, 529, 559, 579, 2310,2311, 5119, 5129, 5159, 5179.

The two images or beams are optically combined, such as with a beamsplitter and viewed directly, or through, but not limited to, aneyepiece or waveguide.

Due to persistence of vision with the method in FIG. 2 and masking withthe method in FIG. 3 the two parts appear as one uniform image 604 inFIG. 6B.

Looking to FIG. 5E, we see a variant of FIG. 5B or 5F with two tiltingoptical slabs 2310 and 2311. The microdisplay, display or projector 2301creates the image or beam and sends the image or beam through a beamsplitter or a rotating mirror 2302. Two identical images or beams aresent from the beam splitter 2302. One image or beam is sent through thelow resolution, large image or wide beam optics 2304, where the highresolution portion is masked off in case of using the method in FIG. 3,and then to the beam splitter 2308, used here as a beam combiner. Theother image or beam is sent from the beam splitter 2302 to a mirror 2303to the high resolution, small image or narrow beam optics 2305, wherethe low resolution image is masked off in case of using the method inFIG. 3. From the small image or narrow beam optics 2305, the image orbeam is reflected off a mirror 2309 to two beam steering elements 2310,2311, to offset the small image or narrow beam in the axis (after itwill be combined with the beam combiner 2308) of the large image or widebeam. In this illustration the beam steering elements are two thickoptical slabs 2310, 2311 that rotate in X and Y axis respectively tooffset the image or beam in these two respective axis. The optical slabs2310, 2311 may each be substituted with a single mirror that rotates inboth axis or two rotating/tilting mirrors, to name a few possiblealternative embodiments. From the second optical slab 2311, the shiftedimage or beam travels to the beam splitter 2308, used here as a beamcombiner. From the beam splitter 2308, the low resolution, large imageor wide beam 2306 and the high resolution, small image or narrow beam2307 travel to the screen 2300 or viewer's retina.

In case of using a beam splitter instead of a rotating mirror as thesteering element 2302 and using the method in FIG. 2, each image eachframe must be blocked or let to pass accordingly before, inside or afterthe optical element 2304, 2305 with an optical or mechanical shuttersuch as an LCD shutter in order to prevent 2304 and 2305 from receivingthe same image of every frame instead of the different images ofdifferent consecutive frames. This is of course not needed if apolarizer beam splitter is used and the polarization of the image can becontrolled each frame before it reaches the beam splitter, such as witha switchable liquid crystal polarization rotator.

In FIG. 6A, the illustration shows rectangles representing individualpixels 601. FIG. 6B shows an illustration with individual pixelsdisplaying an actual image 604.

With tilting/rotating mirrors and rotating wedge (Risley) prisms, theprojection beam or image is steered and gets a perspective distortion,as seen in FIG. 7B, and some optical aberrations which get progressivelyworse as the image or beam is steered farther away from the center. Tofix the perspective distortion the image 702 must be pre-distorteddigitally which reduces the possible size of the high resolution smallimage and the number of utilized pixels significantly.

Also, if there is any inaccuracy or precision issues during positioning,it is visible as a very apparent distortion and seam as the digitaldistortion and image or projection beam do not match the currentpositioning by the mirror, prism or other tilting element, as seen inFIG. 8A.

FIG. 7A is an original image 701, and FIG. 7B is a perspective distortedimage 702.

In FIG. 8A, the correct image 801 is seen. In the image on the right 802(FIG. 8B) the digital imaging and image positioning and distortionmismatch which causes distortion and seam between the two image parts isseen.

With shifting/offsetting the image or beam instead, these issues do nothappen.

The beam or image can be shifted by, but not limited to, twotilting/rotating optical slabs, one for each axis, two dual axistilting/rotating mirrors such as Optotune™ MR-15-30-PS-25x25D or fourtilting/rotating mirrors (two per axis).

In FIGS. 9A-D, an optical slab 902 is a glass slab or a plastic polymerslab clear in the visible spectrum which allows to shift/offset an imageor projection beam 903.

Both an image as well as a projection beam 903 may be shifted with thismethod. The latter allows to have the slabs 902 relatively small whichcan direct the projection beam to projection optics which can produce alarge projected image not requiring much more magnification by theeyepiece lens, waveguide or similar optics in a head-mounted displaydevice.

However, an image may be shifted by this method as well when themagnification can be performed by the eyepiece optics, limited amount ofshifting is needed or limited amount of magnification is needed by theeyepiece lens, waveguide or similar optics.

In FIG. 9B we see a 20×20×20 mm PMMA (Poly(methyl methacrylate)) polymeroptical slab 902 with a collimated 5 mm wide 638 nm wavelength beam 903passing through it and being shifted. In this example the slab can tilt+34 degrees (the range is ±34 degrees) and offset the beam by up to 8.04mm. Considering a situation where such a beam later goes through aprojection lens and the 5 mm beam is meant to cover 20 degrees of thefield of view when looking through the eyepiece or waveguide, a 16.08 mmshift would allow to move the high resolution image which the beamcontains by over 64 degrees or more which is more than the average humancan comfortably rotate their eyes.

In FIG. 9B the optical slab 904 is tilted −34 degrees to offset the beam903 8.04 mm downwards.

Two of such slabs 902,904 will be needed, as seen in FIG. 5E, rotatingin different axis to allow to shift the beam 903 in both axis, or havingan optical component such as a Dove prism or an identical mirrorassembly between two slabs 902, 904 allowing them to rotate in the sameaxis.

The illustration is just for example purposes and different materialsand sizes for the slabs 902, 904, dimensions for the beams 903 androtation ranges are possible.

Slight dispersion of an RGB image or projection beam 903 caused by theoptical slab 902, 904 can be compensated for by digitally offsettingeach color channel by several pixels accordingly. Since offsetting willneed to be done only to one or two color channels with higher refractiveindex, one or two color channels won't be able to reach the same offseton the edges of the image or projection beam 903 which may require todigitally or optically crop the image or projection beam 903 slightly onthe edges so the pixels in each color channel can be offset as much asis required to undo the separation of the color channels caused bydispersion. This loss of pixels on the edges is still negligiblecompared to loss of pixels/detail due to correction of a perspectivedistortion from previous embodiments.

With the above example at the extreme ±34 degree slab tilt the angle ofrefraction at 445 nm wavelength is ±21.9 degrees and at 638 nmwavelength is ±22.1 degrees. This results in 0.06 mm dispersion betweenthe red and blue color channel of the image or projection beam 903.Assuming the resolution of this 5 mm wide image or projection beam 903is 1080 pixels by 1080 pixels, this amounts to 0.06×1080/5=12.96 pixels.Sacrificing 13 pixels on each edge of the beam 903 will allow to offsetthe color channels digitally to undo the effect of dispersion at anyangle.

Specifically looking to FIG. 9A, we see the beam 903 moving through theair 901 to the slab 902. Since the slab 902 is perpendicular to the beam903, the beam 903 goes straight through the slab 902.

In FIG. 9B, the slab 904 is tilted −34 degrees, causing the beam 903 tobe offset 8.04 mm downwards.

In FIG. 9C, the slab 902 is tilted +34 degrees, causing the beam 903 tobe offset 8.04 mm upwards.

In FIG. 9D, there are two views of a single slab 902, 904 superimposedover each other to illustrate how much the beam offsets from one angleto the other. The slab view 904 is tilted −34 degrees, causing the beam903 to be offset 8.04 mm downwards while slab view 902 is tilted +34causing the beam 903 to be offset 8.04 mm upwards. Thus the beam 903 maybe offset up and down, creating images or beams at most 16.08 mm apart.

As seen in FIG. 10A and FIG. 10B, the slabs 902, 904 can also be swappedwith 2d mirrors (dual axis tilting/rotating mirrors such as Optotune™MR-15-30-PS-25x25D) or two mirrors 1001, 1002 or 1003, 1004. This is asavings in cost traded off with bigger space requirements. On the otherhand, dispersion is not an issue with mirrors.

In FIG. 10A the mirrors are tilted at 45 degrees 1001, 1002 and 40degrees 1003, 1004 in FIG. 10B.

Two 2d mirrors rotating in two axis or four mirrors 1101, 1102, 1103,1104 are required to shift the beam or image in two axis as seen in FIG.11.

In FIG. 11, both mirrors 1101, 1102 have a top-down view purely forillustrative purposes, the second set of mirrors 1103, 1104 are inanother axis.

FIG. 12 shows another embodiment. Either the second set of mirrors 1204,1205 can be flipped and rotated in another axis or to save space in oneaxis a Dove prism 1203 or an equivalent mirror assembly may be placedbetween the two 2d mirrors or mirror pairs 1201, 1202 and 1204, 1205 toflip the axis of the offset performed by the previous set and have themirrors and the components which shift/offset them in the same axis.

In FIG. 12 we see the path the ray travels when using the Dove prism1203 (The Dove prism proportions and angle are not accurate in thisdrawing, nor is the path the ray travels inside the Dove prism itself).

Since the smaller high resolution part in the final image can be smallerthan it could be without the use of these methods, thevariable-resolution screen method and apparatus described here allows toachieve more resolution visible in one or more parts of the final imagethan is possible with the display, microdisplay or projector when usedwithout the method described here.

This allows to achieve a variable-resolution screen, such as ahead-mounted display screen which uses as little as only onemicrodisplay, display or projector or one per eye with a high pixel orscanline density in the center of the field of view of the viewer andless in the periphery.

By adding eye tracking via, but not limited to, gaze tracking cameras orelectrodes, the smaller high resolution part can be moved on the finalimage or screen on the bigger low resolution part where the viewer'sfoveal view is at any given point in time. This allows to always havemore pixels or scanlines concentrated in the foveal and optionally alsoin the near peripheral view of the viewer at any given point in time.

Optionally the positioning of the bigger low resolution part can beachieved the same way the positioning of the smaller high resolutionpart, for example to have pixels only in the field of view of theviewer's eye and not the total field of view of the viewer which takesinto account eye rotations.

There can also be more than two parts, such as three, one for the fovealview, one for near peripheral and one for far peripheral and they can becombined the same way as mentioned above.

Those skilled in the art will understand that the order of some elementsin the diagrams can be changed and more can be added, such as shiftingboth large and small images or beams together after they are opticallycombined, or adding more elements for creating more smaller or biggerparts on the final image.

Variable-Resolution Screen with No Moving Parts

In a further embodiment, a variable-resolution screen is achieved bycreating and digitally and optically positioning a small and highresolution image or projection over a large low resolution image orprojection with no mechanically moving parts.

The image source for the at least one large low resolution part 201 andat least one small high resolution part 202 can be the samemicrodisplay, display or projector with consecutive frames (frame n andframe n+1) distributed between the two or more parts 203, 204 of thefinal image or beam (see FIG. 2). Or the parts of the images of themicrodisplay, display or projector could be optically split into two301, 302 or more and allocated between the at least one large lowresolution part 303 and at least one small high resolution part 304, asin FIG. 3. Alternatively, the at least one large low resolution part andat least one small high resolution part can have a differentmicrodisplay, display or projector as image source each as in FIG. 13.

See FIG. 3, where a single 16:9 aspect ratio microdisplay or display issplit into two parts, for example 1920×1080 pixel microdisplay ordisplay split into a small 1080×1080 pixel high resolution part 301 anda large 840×1080 pixel low resolution part 302 (the latter may then beoptically flipped 90 degrees for a better aspect ratio).

The lack of mechanically moving parts provides several advantages:

First, eliminating moving parts eliminates the sensitivity to vibration,misalignment, mechanical failure, audible noise or any other issuesassociated with using mechanically moving parts.

Second, repositioning of the small high resolution part can take as lowas few microseconds to few milliseconds, based on the speed of theoptical masking element used as described below. By contrast it isdifficult to get actuators to rotate a mirror, prism or slab as fast asthe saccadic movement of the human eye while keeping such a motor assmall as possible for a wearable device.

Third, positioning takes equal amounts of time irrespective of the newposition the small high resolution part has to be positioned to.

At first, an image or projection beam is optically duplicated across thewhole or most of the screen or the viewer's retina or part of the screenthe human eye can rotate and focus at.

This can be achieved by, for example, the use of lens arrays. Forillustrative and purposes of showing an example a single or double sidedlens array is used, however a multi-element lens and/or lens array setupis required to reduce optical aberrations in the duplicated images orvideo projections.

FIG. 13 shows a two microdisplays, displays or projectors 1301, 1302embodiment using a lens array. The large image or wide beam is createdby the first microdisplay, display or projector 1301 and sent directly(or through a large image or wide beam optics) to the final image 1305.The second microdisplay, display or projector 1302 creates the smallimage or narrow beam, sending it to the lens array (or other duplicationelement) 1303 and then to an optical masking element 1304 to mask off(hide) the duplicates in the area outside of the one duplicate image tobe shown. The image or beam then proceeds to the final image 1305 whereit is combined with the large image or wide beam from the firstmicrodisplay, display or projector 1301.

FIG. 14 shows a similar embodiment, using a single microdisplay, displayor projector 1401. The image or beam proceeds from the microdisplay,display or projector 1401 to an image or beam steering element 1402. Thesteering element 1402 splits the image or beam, with the large imageportion of the final image or beam sent directly (or through a largeimage or wide beam optics) to the final image 1405 (in some embodiments,such as in FIG. 3, the image is masked to extract small and large imageportions accordingly first). The small image portion of the final imageor beam is sent to the lens array (or other duplication element) 1403,and then to the optical masking element 1404 to mask off (hide) theduplicates in the area outside of the one duplicate image to be shown.This small image or narrow beam is then combined with the large image orwide beam from the steering element 1402 to form the final image 1405.

FIG. 15 shows the simplest setup of how display, microdisplay orprojection beam can be duplicated this way and FIGS. 16A and 16B showthe simulated result.

In FIG. 15, the image source (display, microdisplay or projector) 1501sends the image to a lens 1502 which sends it to the aperture stop 1504.The image or beam then proceeds to the lens array 1503 and then to thescreen 1505 or viewer's retina.

FIGS. 16A and 16B show the simulated result. FIG. 16A is the originalimage from the display, microdisplay or projector 1601 and FIG. 16B isthe resulting image on the screen or viewer's retina 1602.

FIG. 17A shows a simple setup with one possible position of the opticalmasking element. 1701 is a microdisplay, display or projector, 1702 isthe light cone (beam) of a single pixel from 1701. 1703 is a simplifiedillustration of a multi-element lens. 1704 is the first lens array whichfocuses the pixel light cones (beams) to pixels on a LCD microdisplayoptical masking element 1705 on an intermediate image plane and 1706 isthe second lens array which again focuses the pixel light cones on thefinal image plane on a projection screen 1707 or the viewer's retina.The second lens array 1706 can also be replaced with other optics suchas an ordinary projection lens or eyepiece lens.

FIG. 17B shows a reflective microdisplay such as LCoS or DLP used forthe optical masking element. 1711 is a microdisplay, display orprojector generating the image or beam, 1712 is a light cone (beam) of asingle pixel from 1711, 1713 is a simplified illustration of amulti-element lens, 1714 is the first lens array which focuses the pixellight cones (beams) to pixels on a LCoS microdisplay optical maskingelement 1715 on an intermediate image plane and 1717 is the second lensarray which again focuses the pixel light cones (beams) on the finalimage plane on a projection screen 1718 or the viewer's retina. Apolarizer beam splitter or a PBS (polarizer beam splitter) cube 1716 isused to redirect the image or beam reflected off the LCoS microdisplayoptical masking element 1715 90 degrees to the side rather than back tothe first lens array. The second lens array 1717 can also be replacedwith other optics such as an ordinary projection lens or eyepiece lens.With DLP microdisplay a TIR or RTIR (total internal reflection) prismcan be used in place of the polarizer beam splitter or PBS (polarizerbeam splitter) cube 1716.

FIG. 17C shows that it is also possible to use a display, notmicrodisplay, such as an LCD display with its reflective and backlightlayers removed as the optical masking element. 1721 is a microdisplay,display or projector generating the image or beam, 1722 is a light cone(beam) of a single pixel from 1721, 1723 is a simplified illustration ofa multi-element lens, 1724 is the lens array which focuses the pixellight cones (beams) to pixels on a screen 1727 on an image plane behinda LCD display optical masking element 1726 by reflecting the beam with abeam splitter 1725. The image from second display 1728 also reflectsfrom the beam splitter thus both the second display and the screen areseen by the eye 1720 directly or through an eyepiece or waveguide 1729.Here the screen 1727 is used to display the small high resolution imageand the display 1728 is used to display the large low resolution imageof the final combined image combined by the beam splitter 1725.

Alternatively, it is also possible to use a LCD display with itsreflective and backlight layers removed as an optical masking elementwith a single microdisplay, display or projector (or two, as seen inFIG. 13) generating the image or beam without a second display 1728, asillustrated in FIG. 17D. In case of time-multiplexed approach asdescribed in FIG. 2 a beam splitter 1725 is also not necessary asillustrated in FIG. 20 and FIG. 21.

In the FIG. 17D illustration, the elements for generating a duplicatedimage or beam are not illustrated and are in 1731 which represents amicrodisplay, display or projector or two microdisplays, displays orprojectors with the wide beam and duplicated beam already opticallycombined as described in FIG. 13 and FIG. 14. Light cone (beam) of asingle pixel of the wide beam 1732 and light cone (beam) of single pixelof a duplicate beam 1733 both focus to pixels on a screen 1736 on animage plane behind a LCD display optical masking element 1735 by beingreflected from a beam splitter 1734. The screen 1736 is seen by the eye1738 directly or through an eyepiece or waveguide 1737.

In case of splitting a microdisplay, display or projector into two ormore parts as illustrated in FIG. 3 a beam splitter is needed and also asecond screen as illustrated in FIG. 17E.

In the next illustration, FIG. 17E, the elements for generating aduplicated image or beam are not illustrated and are in 1741 whichrepresents a microdisplay, display or projector or two microdisplays,displays or projectors with the wide beam and duplicated beam alreadyoptically combined as described in FIG. 13 and FIG. 14.

Light cone (beam) of a single pixel of the wide beam 1742 and light cone(beam) of a single pixel of a duplicate beam 1743 focus to pixels on asecond screen 1747 and screen 1746 respectively, the latter on an imageplane behind a LCD display optical masking element 1745 by beingreflected from a beam splitter 1744. The wide beam 1742 passes throughthe beam splitter 1744 and the duplicate beam gets reflected from thebeam splitter 1744 instead due to these beams having differentpolarization (or in the case the beam splitter is a band pass filter ordichroic filter, having different light wavelengths). The screens 1746and 1747 are optically combined with the beam splitter 1744 and seen bythe eye 1749 directly or through the eyepiece or waveguide 1748.

Alternatively, in case of splitting a microdisplay, display or projectorinto two or more parts as illustrated in FIG. 3 both a beam splitter andalso a second screen are not needed similarly to the case oftime-multiplexing as illustrated in FIG. 2, as illustrated in FIGS. 17Fand 17G.

In FIG. 17F the elements for generating a duplicated image or beam arenot illustrated and are in 1751 which represents a microdisplay, displayor projector or two microdisplays, displays or projectors with the widebeam and duplicated beam already optically combined as described in FIG.13 and FIG. 14.

Light cone (beam) of a single pixel of the wide beam 1752 and light cone(beam) of single pixel of a duplicate beam 1753 both focus to pixels ona screen 1756 on an image plane behind a LCD display optical maskingelement 1755 by being reflected from a beam splitter 1754. The screen1756 is seen by the eye 1759 directly or through the eyepiece orwaveguide 1757.

To be able to pass both the wide and duplicated beams through the sameLCD display optical masking element but use the optical masking elementfor blocking only the duplicated beams, instead of a traditional LCDdisplay optical masking element a switchable liquid crystal polarizationrotator display is used which is an LCD display optical masking elementwithout polarizers. A single polarizer 1758, not two as on LCD displayoptical masking elements and displays, is placed before the viewer's eye1759 and in front of the eyepiece or waveguide 1757 or somewhere beforeit or left on the LCD display optical masking element 1755.

The wide beam in this instance is not polarized or in the polarizationstate the polarizer 1758 is not going to filter out after the wide beampasses through the switchable liquid crystal polarization rotator/LCDdisplay optical masking element 1755. The duplicated beam gets masked asexpected by the LCD display optical masking element 1755 and thepolarizer 1758 while the wide beam does not or gets masked where theduplicated beam is not masked.

As mentioned previously the beam splitter 1754 is not necessary and usedfor reasons such as decreasing the physical dimensions of the apparatus.FIG. 17G illustrates the same system as FIG. 17F sans the beam splitter1754.

In FIG. 17G the elements for generating a duplicated image or beam arenot illustrated and are in 1761 which represents a microdisplay, displayor projector or two microdisplays, displays or projectors with the widebeam and duplicated beam already optically combined as described in FIG.13 and FIG. 14.

Light cone (beam) of a single pixel of the wide beam 1762 and light cone(beam) of single pixel of a duplicate beam 1763 both focus to pixels ona screen 1765 on an image plane behind a LCD display optical maskingelement 1764. The screen 1765 is seen by the eye 1768 directly orthrough the eyepiece or waveguide 1766.

To be able to pass the wide and duplicated beams through the same LCDdisplay optical masking element but use the optical masking element forblocking only the duplicated beams, instead of a traditional LCD displayoptical masking element a switchable liquid crystal polarization rotatordisplay is used which is an LCD display optical masking element withoutpolarizers. A single polarizer 1767, not two as on LCD display opticalmasking element and displays, is placed before the viewer's eye 1768 andin front of the eyepiece or waveguide 1766 or somewhere before it orleft on the LCD display optical masking element 1764.

The wide beam in this instance is not polarized or in the polarizationstate the polarizer 1767 is not going to filter out after the wide beampasses through the switchable liquid crystal polarization rotator/LCDdisplay optical masking element without the polarizers 1764. Theduplicated beam gets masked as expected by the LCD display opticalmasking element without the polarizers 1764 and the polarizer 1767 whilethe wide beam does not or gets masked where the duplicated beam is notmasked.

With the optical masking element it is possible to show only one of theduplicate images at a time, however with digital manipulation of thesource frame it is possible to have a digital and optical reconstructionof the original image visible anywhere on the duplicated image arrayarea while hiding everything else with a positional accuracy up to thepixel resolution of the optical masking element and positioning speedequal to the few microsecond to millisecond pixel switching speed of theoptical masking element.

As an example, let's consider each duplicated image being made up for 4parts, 1, 2, 3 and 4, as illustrated in FIG. 18, item 1801. In FIG. 18,the items on the left column illustrate these parts as squares withnumbers while the right column uses actual image parts.

In FIG. 18, 4 of such duplicate images are stacked 1802. If we wanted todisplay only one duplicate in the middle of this array 1802, we wouldn'tbe able to as illustrated in item 1803.

However, if we take the original image 1801, partition it into 4 piecesdigitally and reposition those pieces digitally as in 1804, then we willget the result we want even though we are displaying parts of 4duplicates at once.

The duplicates are then masked and the original image 1801 properlyreconstructed by optical and digital methods as seen in 1805.

Since the optical masking elements discussed such as DLP, LCoS or LCDmicrodisplays or LCD displays are usually not double the resolution ofthe lens array but much more, the images can be partitioned into 4rectangles and rearranged digitally not only at the middle of the imagebut at any desired location on the image as seen in 1901, 1902, 1903,1904 in FIG. 19 with the only limitation being the resolution of thesource image display, microdisplay or projector and the resolution ofthe optical masking element. Of course the visible portion from theoptical masking element cannot be larger than the size of a singleduplicate image from the array.

Head-Mounted Display Embodiments

The above optical designs can work for many different types of image andvideo displays. In head-mounted displays, the small space requirementspresent additional challenges.

FIG. 20 shows a direct embodiment of the mounting of the presentinventions in a head-mounted display. The variable-resolution optics2003 as shown in FIGS. 4A, 4B, 5, 13, 14, 17 produces the highresolution small image 2005 and the low resolution large image 2006 thatare sent directly to the screen 2004. A human eye 2001 looks through alens 2002 or other optics that collects the light 2007 from the image onthe screen 2004.

FIG. 21 shows an indirect embodiment of the mounting of the presentinventions in a head-mounted display. The variable-resolution optics2103 as shown in FIGS. 4A, 4B, 5, 13, 14, 17 produces an image that isreflected off of a mirror 2108. The high resolution small image 2105 andthe low resolution large image 2106 from the mirror 2108 are sent to thescreen 2104. A human eye 2101 looks through a lens 2102 or other opticsthat collects the light 2107 from the image on the screen 2104.

FIG. 22 shows an indirect embodiment with a beam splitter of themounting of the present inventions in a head-mounted display. Thevariable-resolution optics 2203 as shown in FIGS. 4A, 4B, 5, 13, 14, 17produces an image that is reflected off of a mirror 2208. The mirror2208 reflects the light to a beam splitter 2209 which reflects the highresolution small image 2205 and the low resolution large image 2206 ontothe screen 2204. A human eye 2201 looks through a lens 2202 or otheroptics and through the beam splitter 2209 to see the light 2207 from theimage on the screen 2204.

The foregoing devices and operations, including their implementation,will be familiar to, and understood by, those having ordinary skill inthe art. All sizes and proportions used in this description could bescaled up or down or changed without impacting the scope of theseinventions.

The above description of the embodiments, alternative embodiments, andspecific examples, are given by way of illustration and should not beviewed as limiting. Further, many changes and modifications within thescope of the present embodiments may be made without departing from thespirit thereof, and the present invention includes such changes andmodifications.

The invention claimed is:
 1. An optical apparatus for creating avariable-resolution image stream on a screen, the apparatus comprising:a projector connected to a video source, where the projector transmits alight image stream in the form of a high resolution, small imagecomponent and a low resolution, large image component; an image steeringelement that directs the high resolution, small image component and thelow resolution, large image component to a small image optical elementand to a large image optical element; an image separation element thatseparates the high resolution, small image component and the lowresolution, large image component into a high resolution, small imagestream and a low resolution, large image stream; where the small imageoptical element and the large image optical element focus the lowresolution, large image stream and the high resolution, small imagestream on the screen such that the low resolution, large image streamand the high resolution, small image stream appear as thevariable-resolution image stream on the screen.
 2. The apparatus ofclaim 1 wherein the light image stream from the projector is timemultiplexed between high resolution, small image component in a firstframe and the low resolution, large image component in a next frame. 3.The apparatus of claim 2 wherein the image separation element is anoptical shutter.
 4. The apparatus of claim 1 wherein the light imagestream from the projector has the high resolution, small image componenton one part of each image and a low resolution, large image component onanother part of each image.
 5. The apparatus of claim 4 wherein theimage separation element is an optical mask.
 6. The apparatus of claim 1wherein the screen is embedded in a virtual reality headset.
 7. Theapparatus of claim 1 wherein the small image optical element includes alens array.
 8. The apparatus of claim 7 further comprising a maskingdisplay to mask off unused portions of the high resolution, small imagestream from the lens array.
 9. The apparatus of claim 7 furthercomprising a masking microdisplay to mask off unused portions of thehigh resolution, small image stream from the lens array.
 10. Theapparatus of claim 1 further comprising a rotating optical slab to steerthe high resolution, small image stream from the small image opticalelement.
 11. The apparatus of claim 1 wherein the large image opticalelement is a lens that focuses the low resolution, large image stream toan outer portion of a field of view of a viewer.
 12. The apparatus ofclaim 1 wherein the small image optical element is a lens that focusesthe high resolution, small image stream to a center portion of a fieldof view of a viewer.
 13. The apparatus of claim 1 wherein the screen isa viewer's retina.
 14. The apparatus of claim 1 wherein the projector isa microdisplay.
 15. The apparatus of claim 1 wherein the projector is adisplay.
 16. An optical method for creating a variable-resolution imagestream on a screen, the method comprising: creating a light image streamin the form of a high resolution, small image component and a lowresolution, large image component with a projector connected to a videosource; directing the high resolution, small image component and the lowresolution, large image component, with an image steering element, to asmall image optical element and to a large image optical element;separating the high resolution, small image component and the lowresolution, large image component into a high resolution, small imagestream and a low resolution, large image stream with an image separationelement; and focusing, by the small image optical element and the largeimage optical element, the low resolution, large image stream and thehigh resolution, small image stream to form the variable-resolutionimage stream on the screen.
 17. The method of claim 16 wherein the lightimage stream from the projector is time multiplexed between the highresolution, small image component in a first frame and the lowresolution, large image component in a second frame.
 18. The method ofclaim 17 wherein the image separation element is an optical shutter. 19.The method of claim 16 wherein the light image stream from the projectorhas the high resolution, small image component on one part of each imageand a low resolution, large image component on another part of eachimage.
 20. The method of claim 19 wherein the image separation elementis an optical mask.
 21. The method of claim 16 wherein the screen isembedded in a virtual reality headset.
 22. The method of claim 16wherein the small image optical element includes a lens array.
 23. Themethod of claim 22 further comprising masking off unused portions of thehigh resolution, small image stream from the lens array with a maskingdisplay.
 24. The method of claim 22 further comprising masking offunused portions of the high resolution, small image stream from the lensarray with a masking microdisplay.
 25. The method of claim 16 furthercomprising steering the high resolution, small image stream from thesmall image optical element using a rotating optical slab.
 26. Themethod of claim 16 wherein the large image optical element is a lensthat focuses the low resolution, large image stream to an outer portionof a field of view of a viewer.
 27. The method of claim 16 wherein thesmall image optical element is a lens that focuses the high resolution,large image stream to a center portion of a field of view of a viewer.28. The method of claim 16 wherein the screen is a viewer's retina. 29.The method of claim 16 wherein the projector is a microdisplay.
 30. Themethod of claim 16 wherein the projector is a display.